1. Field of the Invention
This invention relates to method and apparatus for holding a drill steel in a drill head assembly and, more particularly, to method and apparatus for sliding a tubular member in the drill head assembly into and out of gripping engagement with the drill steel.
2. Description of the Prior Art
In rock drilling operations, it is conventionally known practice to drill holes in a rock formation by a rotary drill assembly or by a rotary percussion drill assembly. These assemblies include a drill pot that carries a hydraulic motor having a motor shaft rotatably connected to a bevel gear which meshes with another bevel gear rotatably journaled on a support member or hub within the drill housing. It is affixed to a rotatable head or cover, which has a seat into which the shank of a drill steel is received. A drill bit is positioned on the upper end of the drill steel. With this arrangement, rotation of the motor shaft is transmitted to the drill steel to rotate the drill bit.
Generally, the drill assembly is carried by a self-propelled machine that maneuvers the drill pot into position and in a direction to advance the drill bit into the rock formation. For rock drilling operations in an underground mine, the drill assembly is supported by a boom that is pivotally mounted on the front of a mobile frame. Upward movement of the boom moves the drill steel seated in a drill pot into drilling position. The boom exerts upward pressure on the drill assembly to increase the driving thrust of the drill steel. As a result, the drill steel advances vertically into the rock formation to dislodge rock materials and form an elongated bore in the rock formation to receive a mine roof bolt.
The upward force exerted upon the drill assembly by the boom overcomes resistance of the rock structure to rotation of the drill bit. Such conditions establish the need for drill assembly configurations that increase the amount of torque applied to the drill steel and decrease drill steel slippage. Dust is also a problem that causes deterioration of the gearing and bearings of drill assemblies. Therefore extensive seal arrangements are used on the drill head assemblies.
Many examples of drill head assemblies are known in the art. U.S. Pat. No. 5,195,598 discloses a typical drill head assembly for rock drill operations. The drill head assembly includes a rotary drill head having a cover with a flinger that can easily be removed from the drill head assembly. U.S. Pat. No. 3,990,552 discloses a drill head that is part of a rotary percussion drill. U.S. Pat. No. 4,190,116 discloses a rotary drill head that is part of a mine roof bolter.
U.S. Pat. Nos. 5,492,183 and 5,690,183 disclose a drill head unit with a drill chuck. The drill chuck includes a cylindrical central section with steel balls for holding a drill steel in place.
Some drill head assemblies include an actuator and spring that cooperate to position jaws to grip a drill steel. U.S. Pat. No. 3,792,869 discloses a drill head having a chuck apparatus with a plurality of jaws for gripping a drill steel. The jaws are not positioned circumferentially to uniformly grip the drill steel. The chuck apparatus includes springs that cooperate with a jaw actuator to position the jaws to grip the drill steel, but the springs resiliently urge the jaws radially inwardly and outwardly.
U.S. Pat. No. 3,992,019 discloses a drill head having a hydraulic powered drill chuck. A hydraulic powered cylinder drives a collet sleeve. The collet sleeve slides against the chuck jaws. The jaws move in a radial direction to grip the drill steel and are not positioned to circumferentially grip the drill steel. Multiple Belleville springs are disclosed, but the Belleville springs do not resiliently urge the jaws in an axial direction.
U.S. Pat. No. 3,692,320 discloses a hydraulic powered drill chuck assembly. The chuck assembly includes a plurality of cylindrical jaws that clamp against a tubular, cylindrical drill stem rod. Each jaw has an outer tapered surface that slides on an inner tapered surface of a protrusion. However, the outer surface does not circumferentially grip the drill steel and is not a mating surface with the inner tapered surface. U.S. Pat. No. 3,692,320 also discloses a Belleville spring and spring plate; however, the Belleville spring moves the jaws in an outward radial direction and does not slide the jaws in an axial direction.
U.S. Pat. No. 4,416,337 discloses a rotary drill assembly having a rotary motor mounted on a drill head. The drill head includes a housing having an internal cavity for holding a rotatable chuck. The drill chuck includes a socket for receiving the shank of the drill steel. The socket is dimensioned to nonrotatably receive the drill steel shank. There is no provision for adjusting the dimension of the socket to increase the gripping engagement of the shank in the socket.
There is need in a drill head assembly for a chuck having a socket that can be moved into and out of gripping engagement with a drill steel shank to securely retain the drill steel in the chuck in operation and to efficiently move the drill steel into and out of position in the chuck.
In accordance with the present invention there is provided a drill head for holding a drill steel that includes a drill housing having an internal cavity defined by an upper opening and a lower portion with a lower opening extending therethrough. An internal sleeve is axially positioned within the cavity and has a tapered external surface and an axial internal bore for receiving the drill steel in frictional engagement. An external sleeve is coaxially aligned with the internal sleeve in the internal cavity. The external sleeve has an internal tapered surface for mating with the external tapered surface of the internal sleeve. A sliding member is positioned for vertical movement in the lower portion of the internal cavity. The sliding member receives hydraulic pressure through the lower opening for moving upwardly to urge the internal sleeve external surface against the external sleeve in response to the hydraulic pressure. A resilient member provides an opposing force to position the internal sleeve to maintain frictional engagement with the drill steel in the internal bore.
Further in accordance with the present invention, there is provided a drill head for gripping a drill steel that includes a drill housing having an internal cavity defined by an upper opening and a lower portion with a lower opening extending therethrough. An inner tubular member is axially positioned within the cavity and has an internal mating surface for receiving a lower end portion of the drill steel and a tapered mating outer surface. An outer tubular member is axially positioned within the cavity and surrounds the inner tubular member and has a mating tapered inner surface for slidably receiving the outer surface of the inner tubular member. A plunger is positioned within the lower end portion of the cavity for sliding the outer tubular member against the inner tubular member. A piston receives hydraulic pressure through the lower opening of the housing and urges the plunger in an axial direction. A resilient member urges the inner tubular member in an axial direction to grip said drill steel.
Additionally, in accordance with the present invention, there is provided a method for gripping a drill steel that includes the steps of receiving a thrusting force from a piston. A drill steel is inserted into an internal bore within a first tubular member. The thrusting force is transferred to the first tubular member to slide the first tubular member against a tapered mating surface of a second concentric tubular member in an axial direction. An opposing force is applied to the first tubular member to normally maintain the first tubular member removed from gripping engagement with the drill steel.
Accordingly, a principal object of the present invention is to provide a drill head assembly having an inner sleeve for uniformly gripping a drill steel.
Another object of the present invention is to provide hydraulic pressure to slide a tubular member to grip a drill steel.
A further object of the present invention is to position a tubular member to grip a drill steel by sliding the tubular member in response to hydraulic pressure and providing a responsive force with a resilient member.
A further object of the present invention is to provide a drill head assembly to uniformly grip a drill steel.
An additional object of the present invention is to provide a drill head assembly providing a grip for a drill steel having lower slippage.
An additional object of the present invention is to provide a drill head assembly that provides a more efficient amount of torque to the drill steel.
These and other objects of the present invention will be more completely described and disclosed in the following specification, accompanying drawings, and appended claims.